Japanese encephalitis

What is it?

Japanese encephalitis is a viral disease that is spread to humans by infected mosquitoes. The mosquitoes breed in rice fields and become infected with the Japanese encephalitis virus usually by biting infected pigs. The pig is therefore called the reservoir of the infection and the mosquito is called the vector. Man gets the disease by being bitten by an infected mosquito. The disease affects the brain and the spinal cord causing severe complications and in some cases death.

What are the symptoms?

Symptoms usually appear 6-8 days after the bite of an infected mosquito. Mild infections present with symptoms that include fever and headache. More severe infection is marked by quick onset, headache, high fever, neck stiffness, disorientation, tremors, occasional convulsions and paralysis, unconsciousness, tremors and death. It is estimated that of 100 people infected with the virus only 1-5 may be severe enough to be hospitalised.

What are the risk factors?

In India, cases have been reported from all states except Arunachal Pradesh, Dadra, Daman, Diu, Gujarat, Himachal, Jammu and Kashmir. It is less common in the North and West of India and more common in the South and East. Outbreaks in West Bengal, Bihar, Karnataka, Tamilnadu, Assam, Uttar Pradesh, Andhra Pradesh, Manipur and Goa have been reported.

What is the treatment?

Diagnosis is based on tests of blood or spinal fluid. There is no specific treatment for the disease and there are no anti-viral drugs effective against this virus. Care of patients centres on supportive treatment including control of fever, care of the unconscious patient till recovery occurs and treatment of fits. In a good intensive care unit, just looking after the unconscious patient can reduce the mortality to half.

What are the prevention?

A vaccine is recommended for use for travellers to rural areas in Asia where the disease is common. It is recommended only for people who travel in these areas for 4 weeks or more, except in circumstances such as an ongoing outbreak of the disease in that area. All travellers should take steps to avoid mosquito bites. They should take care to stay in well screened rooms, avoid exposure at dawn and dusk and use mosquito repellents on exposed skin. At present vaccination is offered by foreign countries to their citizens entering endemic area including India. In India it could be given mostly to those working with the virus and those entering an epidemic area. The vaccine is not easily available at present. It was being manufactured in India for a while but is not available now in the market.

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